In very rare cases severe metabolic acidosis may cause hypotension, respiratory depression and cardiac arrest. Although rare this cause of shock is important because correction of the metabolic acidosis may be life-saving. Mild metabolic acidosis is relatively common in cases of hypoxia and shock, and is an index of the severity of these. Recurrent metabolic acidosis, which reflects failure of the therapy to control the cause of the acidosis, is a gloomy prognostic sign.